It is proposed to conduct further studies of the extra reactions of certain HL-A antisera with cells of chronic lymphatic leukemia as well as normal cells. The presence of these new alloantigens on normal cells are shown by absorption followed by back-testing against CLL cells, which demonstrate the antigens in the cytotoxic reaction. The new alloantigenic system is serologically defined and is not closely related to the HL-A system. In addition, we shall further conduct studies relating HL-A to delayed hypersensitivity to brain tissue in multiple sclerosis. Finally, extensive participation by our laboratory in the VI Histocompatibility Testing Workshop is planned.